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In Reply to: RE: SOTA Comet and Geo-disc a good match? posted by mbnx01 on February 09, 2016 at 17:38:57
I would recommend an arc protractor rather than a Geo-disc. I feel arc protractors are more accurate than the type you point at the tonearm pivot. Personally, I like to print my own using Conrad Hoffman's "Custom Arc Template Generator for Phono Cartridge Alignment," which can be downloaded at the link below. If you prefer to buy an arc protractor, Ken Willis makes the AccuTrak, which sells for a very reasonable price.
Good luck,
John Elison
Follow Ups:
Have you ever compared the alignment results between a "regular" protractor like the Geodisk or DB Systems vs. the arc protractor you use? Just wondering if using an arc results in the cart/cantilever setup being substantially different.
There shouldn't be any difference at all. However, the slightest deviation in pointing the sight-line exactly at the tonearm pivot introduces significant overhang error and subsequent null-point error. It is much easier to be sure the stylus follows an arc than it is to be sure the sight-line is pointing exactly at the tonearm pivot. Furthermore, all arc protractors have two alignment grids thus providing additional assurance in double checking for correct alignment. There is really no contest between the two types of protractors.In a best case scenario, there will be no difference in alignment between a sight-line protractor and an arc protractor. However, in a less than best case scenario, the arc protractor allows you to double check its accuracy with the arc and its two alignment null-points whereas the Geo-Disc has no way of alerting you to an erroneous alignment with only a single alignment null-point.
The DB Systems protractor is a different story because it has two alignment null-points. You should therefore be able to achieve an accurate alignment. However, since it contains no arc for setting overhang, the alignment process will take longer than with an arc protractor. If you think about it, an arc protractor is simply a two-point protractor like the DB Systems protractor but with the additional feature of an arc for instantly setting and rechecking overhang. There is no need to make alignment comparisons to see that an arc protractor is potentially better and more accurate than other types of protractors.
Best regards,
John Elison
Edits: 02/10/16
Yes, pointing a line at the exact pivot point is somewhat imprecise - at least with my arm, and easier is better. I only use my DB Systems after I set overhang with the Geodisk 'cause doing that with the DB is a PITA.
I'm a fan of Ken's protractors as well. I used to print out my own but cutting out the center hole was tricky. What I did was get an old light colored album like from Grand Funk and print the protractor on transparency paper. Then I centered the spindle hole marking over the spindle hole on the actual album and taped it securly in place. Then I could cut out a hole much larger and the alignment was maintained. This worked really well for me. Cheap as well.
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